Hardened steel roll and composition therefor



United States Patent 3,060,016 HARDENED STEEL ROLL AND COMPUSHTION THEREFOR George F. Melloy, Bethlehem, and Donald E. Wise, Allentown, Pa., assignors to Bethlehem Steel Company, a corporation of Pennsylvania N Drawing. Filed Jan. 23, 1961, Ser. No. 83,917 8 Claims. (Cl. 75-126) This invention relates to rolling mill rolls and more particularly to forged and hardened steel rolls of novel compositions.

Although it has heretofore been possible to produce a hardened steel roll having resistance to premature failure While at the same time having a hard surface and a certain depth of hardness, there is always the need to produce a roll having greater resistance to premature failure, greater depth of hardness, etc. Premature failure usually occurs either during the quenching operation itself or shortly thereafter, although it may occur during transit to the customer, and even after the rolls are in normal service. Premature failure, which is believed to be caused mainly by residual stresses imparted to the steel by the heat treating operation, may be accompanied by an explosive force, and flying fragments of steel may damage costly equipment or injure personnel. Hardened steel rolls should preferably be free from a hardness resurgence zone beneath the hardened surface. Hardness resurgence is believed by many to be a cause of spalli'ng.

Prior art solutions, including the provision of various alloy compositions and heat treatments, have failed to provide a steel roll having an optimum combination of all of the above mentioned properties. The grade of steel used in hardened steel rolls in the past and generally accepted as having the best combination of desired properties is typically, with but minor variations, of the following compositions:

Percent Carbon .87- .93 Manganese .30 .45 Silicon .20 .35 Chromium 1.65-1.85 Vanadium .08- .10 Molybdenum .20- .30

Hardened steel rolls made of this typical roll steel are subject to premature failures. Furthermore, the rolls frequently have a hardness resurgence zone, and failure of the roll due to spalling occasionally occurs. In addition, although the depth of hardening is good, a greater hardness penetration is desirable.

It is therefore an object of the invention to provide a hardened steel roll having improved resistance to premature failure, full maximum desired hardness, increased depth of hardening, gradual transition for a hard outer zone to a soft inner zone, and freedom from a hardness resurgance zone.

It is a further object of the invention to provide a forged and hardened steel roll having improved properties and novel compositions.

We have discovered that the foregoing objects can be attained by the use of alloy steels containing a novel combination of carbon, manganese, chromium, and molybdenurn within certain well defined limits.

The broad range of our improved roll steel is as follows:

Percent Carbon .65 .80 Manganese .10 .35 Chromium .60-1.l0 Molybdenum .45- .70 Balance Essentially iron By balance essentially iron we do not wish to exclude those elements usually found in residual amounts in commercial steels, for example small quantities of nickel, copper, etc., customarily found in steel scrap, or elements which may be added during the steelmaking process. For example, the steel is ordinarily killed by adding small quantities of silicon, e.g. .20 to 35%. Vanadium may be added in small amounts, e.g. up to .15 to make the steel more uniform. Hardened steel rolls having compo sitions within this broad range have a combination of properties superior to prior art roll steels. The resistance to premature failure is superior to the best prior roll steels, the desired surface hardness is attainable, and steels of this invention have a greater depth of hardening than the aforementioned typical roll steel, and are free from a zone of hardness resurgence.

As to the upper and lower limits of the elements contained in our new roll steels, we have found that decreasing the carbon content below .65 decreases the surface hardness to below the desired level. Increasing the carbon to substantially above .80% decreases the resistance to premature failure. A minimum of .10% manganese is necessary for ease in forging the steel, while increasing the manganese above about .35 tends to decrease the resistance to premature failure. At least .60% chromium insures a suificient depth of hardening and desirable resistance to premature failure. Increasing the chromium above about 1.10% increases the tendency to premature failure. A minimum of .45% molybdenum is considered necessary to insure the desired depth of hardness, while a molybdenum content above about .70% increases the tendency toward premature failure.

While we have described our new alloy in terms of the effects of the individual elements, we believe the invention resides in the particular combination of these elements. A preferred range of compositions which yields the optimum combination of desired properties is as follows:

Percent Carbon .70.75 Manganese .15.25 Chromium .70.85 Molybdenum 60-.70 Balance Essentially iron Hardened steel rolls of these compositions have a maximum residual stress lower than that of prior roll steels of equal hardness. Furthermore, the steels of the invention exhibit no zone of hardness resurgance and attain the desired surface hardness, while the depth of hardening is greater than that realized with the aforementioned typical roll steel. In addition, the steels of the invention show unusual freedom from segregation and material defects.

As a specific example of our alloys and the best contemplated mode of producing them, a heat was melted in an electric furnace and vacuum cast into a 62" ingot. The ladle analysis was:

Percent Carbon .72

Manganese .32

Chromium .85

' Molybdenum .67 Silicon' .20

Vanadium .10

Phosphorus .022

Sulfur .008

An 18%" roll was forged from the ingot, and the roll was equalized, normalized, and annealed according to standard metallurgical practices. The roll was then roughmachined to its approximate final size. The roll was rough ground and sonic inspected prior to hardening,

and was then hardened according to normal practice. This practice comprised preheating the roll to 700 F. and equalizing, further preheating the roll to 1250 F. and equalizing, uniformly austenitizing the roll at 1550 E., and quenching in a submerged Water spray. The roll was then tempered at 300 F. for 120 hours. Following the heat treatment, the roll was machined and ground to final dimensions.

The roll had a final surface hardness of 95/98 Shore For most applications, the lower limit of useful hardness in hardened steel rolls is generally believed to be about 80 Shore C. The depth of useful hardness, on this basis, in this roll was 0.8", while the depth of useful hardness of the aforementioned typical roll steel, determined on the same basis, was slightly over 0.5". Furthermore, the roll had a maximum residual stress about 28% lower than that of the typical roll steel.

Hardened steel rolls having compositions within the broad ranges of the invenion have better resistance to premature failure than the best steel rolls of the prior art, while rolls having the preferred composition have much better resistance to premature failure. All steels of the invention, i.e. those of both broad and preferred ranges, have no zone of hardness resurgance. Furthermore, these steels can be hardened to the desired surface hardness, and the depth of hardening is improved. In addition, the steels are unusually free from segreagtion and material defects and can be produced at less cost.

Although we have described our invention in considerable detail, we do not wish to be limited to the exact compositions shown and described, but may use such substitutions, modifications or equivalents thereof as are embraced within the scope of our invention or as pointed out in the claims.

We claim:

1. A steel alloy consisting essentially of .65 to .80% carbon, .10 to .35% manganese, .60 to 1.10% chromium,

.45 to .70% molybdenum, and the balance being essen-' tially iron.

2. A forged and hardened steel roll, said roll consisting essentially of .65 to .80% carbon, .10 to .35 manganese, .60 to 1.10% chromium, .45 to .70% molybdenum, and the balance being essentially iron.

3. A steel alloy consisting essentially of .70 to .75% carbon, .15 to 25% manganese, .70 to .85 chromium, .60 to .70% molybdenum, and the balance being essentially iron.

4. A forged and hardened steel roll, said roll consisting essentially of .70 to .75 carbon, .15 to 25% manganese, .70 to .85 chromium, .60 to .70% molybdenum, and the balance being essentially iron.

5. A steel alloy consisting essentially of .65 to .80% carbon, .10 to 35% manganese, .60 to 1.10% chromium,

. .45 to .70% molybdenum, vanadium up to .l5%, and

the balance being essentially iron.

6. A forged and hardened steel roll, said roll consisting essentially of .65 to .80% carbon, .10 to 35% manganese, .60 to 1.10% chromium, .45 to .70% molybdenum, vanadium up to ,15%, and the balance being essentially iron.

7. A steel alloy consisting essentially of .70 to .75% carbon, .15 to 25% manganese, .70 to .85% chromium, .60 to .70% molybdenum, vanadium up to .l5%, and the balance being essentially iron.

8. A forged and hardened steel roll, said roll consisting essentially of .70 to .75% carbon, .15 to .25 manganese, .70 to .85% chromium, .60 to .70% molybdenum, vanadium up to .15%, and the balance being essentially iron.

References Cited in the file of this patent FOREIGN PATENTS 457,872 Great Britain Dec. 2, 1936 

1. A STEEL ALLOY CONSISTING ESSENTIALLY OF .65 TO .80% CARBON, .10 TO .35% MANGANESE, .60 TO 1.10% CHROMIUM, .45 TO .70% MOLYBDENUM, AND THE BALANCE BEING ESSENTIALLY IRON. 